icon

Arguments:
window &optional smallp

Returns (or sets with setf)
the icon that is used to represent window. The
value must be an icon handle (a non-negative integer), which is either
the value of one of the built-in icons such as error-icon, a handle returned by
calling extract-icon-from-file or create-icon-handle at
runtime, or nil to use the default icon of
the executable file (which is the Franz icon in the development lisp).

When the icon is set to one of the built-in icons, both the large and
small versions of the icon are set with one call, regardless of the
value of smallp (a single handle is used for both
sizes). Otherwise, a true
smallp indicates the 16 by 16 version of the icon
and a null smallp indicates the 32 by 32 version of the icon. A
window's titlebar uses the small version. The ALT-TAB window for
switching between applications uses the large version by default (for
top-level non-owned windows only).